EM waves have been used in various applications to supply energy to objects. In the case of radio frequency (RF) radiation for example, EM energy may be supplied using a magnetron, which is typically tuned to a single frequency for supplying EM energy only in that frequency. One example of a commonly used device for supplying RF energy is a microwave oven. Typical microwave ovens supply EM energy at or about a single frequency of 2.45 GHz.
Microwave ovens are known to apply energy at a non-uniform manner. It has been suggested that uniformity of RF heating may be improved if energy is applied at many different frequencies. It was also suggested that if a same amount of energy is absorbed at each frequency, this may enhance uniformity.